@基于VSC- HVDC的风电场与电网连接研究

D and environmental
This work was supported in part by National Natural Science Foundation of China (No. 50877027) and the Fundamental Research Funds for the Central Universities (No. 1OMG04). The authors are all with the School of Electrical and Electronic Engineering, North China Electric Power University,Baoding 071003, Hebei, P.R.China (e-mail: kangjinliang_ncepu@. hfliang@. ligy@,zhouming@,happyleaf7@). 978-l-4244-5940-7/10/$26.00©2010 IEEE
2010 International Conference on Power System Technology
Research on Grid Connection of Wind Farm Based on VSC-HVDC
Jinliang Kang, Haifeng Liang, Member, IEEE, Gengyin Li, Member, IEEE, Ming Zhou, Member, IEEE, and Hua Yang
With the development of power electronics and vector control technology, DFIG has become a mainstream turbine type of megawatt wind turbine in the recent years. In this paper, all wind turbines use DFIG. There are four kinds of topology for VSC-HVDC connection of wind farm in figure. 1. Fig. l(a) shows a single input single output (SISO) two-port topology [6]. This topology is suitable for small-scale wind farm in which wind turbines are concentrative. All wind turbines constitute a single wind turbine group and run at the same wind speed; when the scale of wind farm is large, in order to improve the wind energy capture rate, wind turbines are divided into several groups according to their close geographical location and the almost same wind speed. Each group can run at the different wind speed. Large-scale wind farm can adopt the topology in Fig. 1(b). Fig. 1(b) can be simply treated as multiple SISO VSC-HVDCs in parallel; for large-scale wind farm, multi-port VSC-HVDC topology can also be used, as shown in Fig. 1(c), Fig. 1(d). In the multi input single output (MISO) topology of Fig. l(c) [7]-[8], each wind turbine group can run in their respective average wind speed and wind power will be transmitted into a single grid through only one DC bus. Compared with the topology in Fig. I (b), the topology only requires a DC bus and an inverter. It reduces the number of inverter and the DC line greatly and improves the economics of the system; Fig. l(d) shows a multi input multi output (MIMO) multi-port topology [9]-[11]. The control system of the topology is more complicated. However, it brings greater flexibility and adjustment capacity for large­ scale wind farms. Large-scale wind farm can be connected to several grid or passive load through shared DC bus by MIMO topology. Power flow optimal scheduling can be realized and power system stability can be enhanced.
WIND FARM TO GRID
Index
LVRT
Terms-Wind
farm,
VSC-HVDC,
gy,
DFIG,
I.
INTRODUCTION
ue to its large development capacity, mature technology friendliness, Wind generation has become the fastest growing energy among the renewable energy. Most traditional wind farm are connected to the nearest AC grid by AC transmission technology. However, with the increasing of transmission distance and capacity, AC transmission brings more and more problems. For example, the loss of AC transmission is serious, the grid voltage is unstable, and the system's power quality is worse. Because of the existence of AC cable charge current, AC transmission is not fit for offshore wind farms. Thus the AC connection is no longer suitable for wind farm connection to the grid [1]-[2]. With the development of power electronics technology, Voltage source converter based HYDC (VSC-HVDC) transmission technology developed rapidly. Compared with the AC connection and classical HVDC connection, VSC­ HYDC has the following advantages [3]-[5]: VSC-HVDC not only can control the active power and reactive power independently, but also supply power directly to the weak power system and passive network; VSC can play the role of reactive power compensator, compensate AC bus reactive power dynamically and stabilize the AC bus voltage; VSC is more convenient and faster to realize the power flow reversal characteristics make the VSC-HVDC is more consistent with and conducive to build multi-terminal DC system. VSC-
HYDC can improve system voltage stability. It is not subject to transmission distance and transmission capacity. It can be used for grid-connection of large offshore wind farm. So VSC-HVDC is the ideal transmission technology for the connection of the wind farms to the power system In this paper the topology of VSC-HVDC and control strategy were mainly studied. Double fed induction generator (DFIG) and VSC-HVDC were modeled in PSCADIEMTDC software. Simulation results were presented to illustrate the effectiveness of the control strategy. II. THE TOPOLOGY OF VSC-HYDC FOR THE CONNECTION OF